Dexamethasone prevents vascular damage in early-stage non-freezing cold injury of the sciatic nerve

Abstract

Non-freezing cold injury is a prevalent cause of peripheral nerve damage, but its pathogenic mechanism is poorly understood, and treatment remains inadequate. Glucocorticoids have anti-inflammatory and lipid peroxidation-inhibiting properties. We therefore examined whether dexamethasone, a synthetic glucocorticoid compound, would alleviate early-stage non-freezing cold injury of the sciatic nerve. We established Wistar rat models of non-freezing cold injury by exposing the left sciatic nerve to cold (3-5°C) for 2 hours, then administered dexamethasone (3 mg/kg intraperitoneally) to half of the models. One day after injury, the concentration of Evans blue tracer in the injured sciatic nerve of rats that received dexamethasone was notably lower than that in the injured sciatic nerve of rats that did not receive dexamethasone; neither Evans blue dye nor capillary stenosis was observed in the endoneurium, but myelinated nerve fibers were markedly degenerated in the injured sciatic nerve of animals that received dexamethasone. After dexamethasone administration, however, endoneurial vasculopathy was markedly improved, although damage to the myelinated nerve fiber was not alleviated. These findings suggest that dexamethasone protects the blood-nerve barrier, but its benefit in non-freezing cold injury is limited to the vascular system.

Keywords: blood-nerve barrier; dexamethasone; hypothermia; nerve regeneration; neural regeneration; non-freezing cold injury; peripheral nerve injury; sciatic nerve.

Figure 1

Effect of dexamethasone on the concentration of Evans blue in the sciatic nerve after non-freezing cold injury. Data are expressed as the mean ± SD (n = 8 rats per group). *P < 0.05, vs. injury group; #P < 0.05, vs. contralateral side (completely randomized analysis of variance with paired t-test pairwise comparison).

Figure 2

Representative cross-sections of sciatic nerves (Evans blue staining, × 40) 1 day after non-freezing cold injury. Dexamethasone inhibited the dispersion of Evans blue after injury. (A) Control (contralateral) sciatic nerve, showing no leakage of red fluorescence from the endoneurium. (B) Damaged sciatic nerve, showing a large amount of red fluorescence in the endoneurium. (C) Damaged sciatic nerve after dexamethasone treatment, showing markedly less red fluorescence leaking from the endoneurium than observed in the injured sciatic nerve without dexamethasone treatment.

Figure 3

Effects of dexamethasone on the morphology of the sciatic nerve 1 day after non-freezing cold injury (toluidine blue staining, × 400). (A) Contralateral sciatic nerve. (B) Damaged sciatic nerve, showing degeneration identified by empty or dark axons and vascular endothelial cell swelling (black arrow). (C) Damaged sciatic nerve after dexamethasone treatment; axons showed signs of degeneration, but no endoneurial microvessel swelling or stenosis was observed (black arrow).

Figure 4

Effects of dexamethasone on the ultrastructure of the sciatic nerve after non-freezing cold injury (toluidine blue staining, transmission electron microscope). (A) Endoneurial microvessels of the sciatic nerve on the contralateral side appeared normal, and were surrounded by normal myelin sheath (× 2,000). (B) Myelinated and unmyelinated nerve fibers on the contralateral side appeared normal (× 8,000). (C) After non-freezing cold injury, tight junctions in the endoneurial vascular endothelial cells of the sciatic nerve remained intact (red arrow), and proliferation of vascular endothelial cells was observed (× 6,300). (D) In the injury group, swollen axon membranes, compressed axons (red arrow), and mitochondrial pyknosis were observed (× 8,000). (E) In the dexamethasone treatment group, the endoneurial capillary cavity appeared normal, no endothelial cell proliferation was observed, and red blood cells passed normally through the lumen (× 25,000). (F) In the dexamethasone treatment group, the sheath layer of myelinated nerve fibers was loose, and the axon was degenerated and compressed, but unmyelinated nerve fibers appeared normal (× 6,300).